Preparation method of conductive sponge having effect of shielding electromagnetic wave

ABSTRACT

A preparation method of a conductive sponge includes the following steps. First, a sponge substrate is dipped in a metal solution and then taken out. A first drying process is performed. Next, the sponge substrate plated with metal particles is dipped in a carbon nanomaterial suspension and then taken out. Then, a second drying process is performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to a preparation method of a conductive sponge, and more particularly, to a preparation method of a conductive sponge having the function of shielding electromagnetic wave.

2. Description of Related Art

A conductive sponge is generally attached to the internal electronic components of various electronic products used in everyday life such as mobile phones, notebook computers, and tablet computers, so as to achieve the objects of protection from static electricity, prevention of electromagnetic interference, and reduction of electromagnetic radiation. The conductive sponge preferably has good elasticity, low conduction resistance, and good grounding performance. As electronic products become lighter and smaller, it is preferred that the conductive sponge can have any size.

The fabrication method of the ordinary conductive sponge includes the following two methods. First, a conductive material can be added during the foaming fabrication process of a sponge substrate. However, mass production is not readily achieved via such method due to complex process. Moreover, a chemical vapor deposition (CVD) process or a physical vapor deposition (PVD) process can be used to cover a metal such as nickel or copper on the sponge substrate. However, the CVD process readily causes pollution issues and is largely discontinued. The PVD process must to be performed under a vacuum condition, and consumption of metal target is high. Therefore, production cost of the PVD process is high. Moreover, when the thickness of the sponge substrate is too great, the plated material (such as nickel or copper) is not readily entered deep inside the sponge substrate, and therefore the plating penetration ratio is poor. As a result, a conductive sponge made by a PVD process is limited in thickness.

SUMMARY OF THE INVENTION

The invention provides a preparation method of a conductive sponge. The preparation method has a simple process and can fabricate a conductive sponge of any thickness.

A preparation method of a conductive sponge of the invention includes the following steps. First, a pretreatment step is performed on a sponge substrate, and then the sponge substrate is dipped in a metal solution and then taken out. A first drying process is performed on the sponge substrate dipped in the metal solution. The sponge substrate is dipped in a carbon nanomaterial suspension after the first drying process and then taken out. A second drying process is performed on the sponge substrate dipped in the carbon nanomaterial suspension.

In an embodiment of the invention, the material of the sponge substrate includes melamine, polyurethane, or sponge substrate materials composed of other polymer components.

In an embodiment of the invention, the metal solution includes a silver ion solution, a nickel ion solution, an iron ion solution, a cobalt ion solution, or any metal ion solution.

In an embodiment of the invention, the metal solution includes a silver nitrate solution, a nickel nitrate solution, or other metal compound solutions.

In an embodiment of the invention, the solute of the carbon nanomaterial suspension includes, for instance, carbon black, carbon nanotube, graphene, or carbon aerogel.

In an embodiment of the invention, before the sponge substrate is dipped in the metal solution, a sensitizing treatment is further performed.

In an embodiment of the invention, after the sensitizing treatment is performed and before the sponge substrate is dipped in the metal solution, an activation treatment is further performed.

In an embodiment of the invention, after the second drying process is performed, the sponge substrate dipped in the carbon nanomaterial suspension is further dipped in a polydimethylsiloxane solution and then taken out.

In an embodiment of the invention, after the second drying process is performed, a heat-resistant adhesive covering process is further performed to cover the sponge substrate with a heat-resistant adhesive.

Based on the above, the conductive sponge of the embodiments of the invention can be fabricated via dipping and drying processes. Therefore, the conductive sponge has a simple process and low production cost. Moreover, via the dipping method, a conductive material such as a metal and a carbon nanomaterial can be entered deep inside the sponge substrate and be uniformly distributed. Therefore, the conductive sponge obtained via the preparation method of the embodiments of the invention has good plating penetration ratio and is not readily limited in thickness.

In order to make the aforementioned features and advantages of the disclosure more comprehensible, embodiments accompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of a preparation process of a conductive sponge according to an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a schematic diagram of a preparation process of a conductive sponge according to an embodiment of the invention. Referring to FIG. 1, step S100 is performed, wherein a sponge substrate is provided and some pretreatments are optionally performed on the sponge substrate, such as an etch-cleaning treatment, a sensitizing treatment, and an activation treatment. The sponge substrate is a material having a large number of holes on the inside. The material of the sponge substrate includes melamine, polyurethane, or sponge substrate materials composed of other polymer components.

Specifically, etching can first be performed on the sponge substrate via an etching solution so as to remove impurities attached to the surface (including inside and outside) of the sponge substrate. Then, the sponge substrate is washed with water. The etching solution is, for instance, a sulfuric acid solution, a hydrochloric acid solution, or other acidic solutions.

Next, a sensitizing treatment can be performed on the sponge substrate. In the sensitizing treatment, a solution with reducible metal salt is used for the sponge substrate such that the metal ions are located on the surface of the etched sponge substrate. Specifically, the washed sponge substrate is dipped into a sensitizing solution, wherein the sensitizing solution is, for instance, a mixed solution of tin chloride (SnCl₂) and hydrochloric acid (HCl) in a volume ratio of 1:2.5. When the sponge substrate is dipped in the mixed solution, tin ions are attached to the surface of the holes on the inside of the sponge substrate and on the external surface of the sponge substrate. Ion exchange can be performed on the tin ions in a subsequent treatment to facilitate the performance of the activation treatment.

Next, an activation treatment can be performed on the sponge substrate. In the activation treatment, a noble metal solution is used to perform ion exchange on the sponge substrate such that activating ions are bonded on the surface of the sponge substrate as a catalytic center. The sensitized sponge substrate is dipped in an activating solution, wherein the activating solution is, for instance, a mixed solution of silver nitrate (AgNO₃) and ammonium nitrate solution (NH₄NO₃) in a volume ratio of 1:10. At this point, silver ions can be replaced by tin ions in the sponge substrate such that silver ions are bonded on the surface of the sponge substrate. This step facilitates the subsequent performance of plating a metal (such as silver) on the sponge substrate.

In another embodiment, the activating solution can also be a mixed solution of nickel nitrate (Ni(NO₃)₂) and ammonium nitrate solution in a volume ratio of 1:10. At this point, nickel ions can be replaced by tin ions in the sponge substrate such that nickel ions are bonded on the sponge substrate. This step facilitates the subsequent performance of plating a metal (such as nickel) on the sponge substrate.

In other embodiments, different metal ion solutions can be used for the activating solution, such as solutions containing magnetic metal ions such as iron ions or cobalt ions. In other words, the type of the metal ions of the activating solution can be decided based on the type of the metal to be plated on the sponge substrate. The above embodiments are only exemplary and are not intended to limit the invention.

Then, step S110 is performed, wherein the sponge substrate is dipped in a metal solution and then taken out. In the present embodiment, the activating solution is, for instance, a mixed solution of silver nitrate and ammonia nitrate solution, and the metal solution is, for instance, a silver nitrate solution. In other embodiments, the metal solution includes a nickel nitrate solution or other solutions of a metal to be plated. The concentration and the dipping time of the metal solution are not particularly limited, and those having ordinary skill in the art can decide the dipping time based on the type and the size of thickness of the sponge substrate and the concentration of the metal solution. When dipping, a metal is gradually plated on the sponge substrate such that a metal material is present on the surface of the holes on the inside of the sponge substrate and on the exterior surface of the sponge substrate.

Then, step S120 is performed, wherein a first drying process is performed on the sponge substrate dipped in the metal solution. Specifically, the sponge substrate can be disposed in an oven for baking so as to remove the solvent of the metal solution. As a result, the weight of the sponge substrate is reduced by, for instance, 5 weight percent. Of course, the invention does not require the drying process to include the baking step. In other embodiments, the drying process can also include air blowing or leaving the sponge substrate to dry.

Then, step S130 is performed, wherein the sponge substrate is dipped in a carbon nanomaterial suspension after the first drying process and then taken out. Specifically, the solute of the carbon nanomaterial suspension is, for instance, a conductive carbon material including carbon black, carbon nanotube, graphene, or carbon aerogel. The concentration of the carbon nanomaterial suspension is, for instance, between 0.1 weight percent and 10 weight percent. The dipping time is about 1 minute to 3 minutes. However, the invention is not limited thereto. Those having ordinary skill in the art can decide the dipping time based on the type and the size of thickness of the sponge substrate and the concentration of the carbon nanomaterial suspension. When dipping, a carbon nanomaterial is gradually adsorbed on the surface of the holes on the inside of the sponge substrate and on the exterior surface of the sponge substrate. As a result, a metal and a carbon nanomaterial are coated on the sponge substrate such that a composite material is formed on the sponge substrate.

Then, step S140 is performed, wherein a second drying process is performed on the sponge substrate dipped in the carbon nanomaterial suspension. Specifically, the sponge substrate can be disposed in an oven for baking so as to remove the solvent of the carbon nanomaterial suspension. As a result, the weight of the sponge substrate is reduced by, for instance, 5 weight percent. Of course, the invention does not require the drying process to include the baking step. In other embodiments, the drying process can also include air blowing or leaving the sponge substrate to dry.

At this point, the fabrication of the conductive sponge having a composite material is preliminarily complete, wherein the surface of the conductive sponge has a metal material and a carbon nanomaterial. The metal material has good electron transport capability, thus facilitating the transmission of electrons to the carbon nanomaterial present on the surface of the metal material. After the carbon nanomaterial receives electromagnetic energy, the energy interacts with the conjugate structure of the carbon nanomaterial. As a result, the carbon nanomaterial generates vibration, thus converting the electromagnetic energy into heat and then dissipating the heat. Under the combined effect of the metal material and the carbon nanomaterial, electromagnetic noise can be absorbed and dissipated by the conductive sponge. Moreover, due to the porosity of the sponge substrate itself, after the above treatments, the sponge substrate achieves the function of shielding electromagnetic energy via a multi-reflection mechanism.

In the previous steps, the conductive sponge is mainly made by dipping and baking processes, and therefore the fabrication of the conductive sponge is relatively simple. Moreover, by using a dipping process, the above material can be entered deep inside the sponge substrate. Therefore, the dipping process is not limited by the thickness of the sponge substrate, and a conductive sponge of any size can be fabricated.

Moreover, step S150 can optionally be further performed, wherein the sponge substrate is dipped in a polydimethylsiloxane (PDMS) solution after the second drying process and then taken out. The concentration of the PDMS solution is about 0.1 weight percent to 10 weight percent. The PDMS solution can strengthen the adhesion of the carbon nanomaterial on the skeleton of the sponge substrate and soften the carbon nanomaterial to be elasticity. Then, the sponge substrate can be dried via a third drying process.

Then, step S160 is optionally performed, wherein a heat-resistant adhesive covering process is performed to cover the sponge substrate with a heat-resistant adhesive so as to exert the function of protecting the sponge substrate.

Based on the above, the surface of the conductive sponge of the invention has a metal material and a carbon nanomaterial. The metal material transmits electrons to the carbon nanomaterial absorbed on the surface of the metal material, and the carbon nanomaterial can generate vibration after absorbing electromagnetic energy and thus convert the electromagnetic energy into heat and then dissipate the heat. Moreover, the sponge substrate further has a multi-reflection mechanism after the above treatments are performed. Therefore, under the combined effect of the metal material and the carbon nanomaterial, the conductive sponge can have good function of shielding electromagnetic wave. The conductive sponge further has advantages such as compressibility and the capability of being bent.

Moreover, in the preparation method of the conductive sponge of the invention, the conductive sponge is mainly made by dipping and baking processes, and therefore the fabrication of the conductive sponge is relatively simple and overly complex equipment is not needed. As a result, the production cost of the conductive sponge is low. Moreover, the conductive sponge is suitable for mass production, and issues such as pollution and equipment costs are negligible. Moreover, by using a dipping process, the plating penetration ratio of the metal material and the carbon nanomaterial can be increased, and the dipping process is not limited by the thickness of the sponge substrate. As a result, a conductive sponge of any size can be fabricated. 

What is claimed is:
 1. A preparation method of a conductive sponge, comprising: dipping a sponge substrate in a metal solution and then taking out the sponge substrate; performing a first drying process on the sponge substrate dipped in the metal solution; dipping the sponge substrate in a carbon nanomaterial suspension after the first drying process and then taking out the sponge substrate; and performing a second drying process on the sponge substrate dipped in the carbon nanomaterial suspension.
 2. The preparation method of a conductive sponge of claim 1, wherein a material of the sponge substrate comprises melamine or polyurethane.
 3. The preparation method of a conductive sponge of claim 1, wherein the metal solution comprises a silver ion solution, a nickel ion solution, an iron ion solution, or a cobalt ion solution.
 4. The preparation method of a conductive sponge of claim 1, wherein the metal solution comprises a silver nitrate solution, a nickel nitrate solution, or a copper nitrate solution.
 5. The preparation method of a conductive sponge of claim 1, wherein a solute of the carbon nanomaterial suspension comprises carbon black, carbon nanotube, graphene, or carbon aerogel.
 6. The preparation method of a conductive sponge of claim 1, further comprising, before the sponge substrate is dipped in the metal solution, performing a sensitizing treatment.
 7. The preparation method of a conductive sponge of claim 6, further comprising, after the sensitizing treatment is performed and before the sponge substrate is dipped in the metal solution, performing an activation treatment.
 8. The preparation method of a conductive sponge of claim 1, further comprising, after the second drying process is performed, dipping the sponge substrate dipped in the carbon nanomaterial suspension in a polydimethylsiloxane solution and then taking out the sponge substrate.
 9. The preparation method of a conductive sponge of claim 1, further comprising, after the second drying process is performed, performing a heat-resistant adhesive covering process to cover the sponge substrate with a heat-resistant adhesive. 